Making barrels is pretty easy. Just take some poster card or even a Slotta-Base, a 15mm coupling and use a Hot-Glue-Gun to fix them together. For barrel lids I use a simple method. Spread a puddle of black paint, press a "barrel" in it and then press it on some card. You have a  perfectly round 15mm lid. Of course, you could also use a pencile and draw the 15mm circle or circle around a barrel. Whatever, use then a Nail-Clipping-Scissor to get a round lid. The Nail-Clipper is preformed, so it´s easier to get an accurate circle than with normal scissors. Glue it on with White Glue or Hot Glue

You can decorate the bases as usual with sand and/or Kitty Litter, using stuff from your BitsBox to make it more interesting. One of my open barrels actually has a SpaceMarine arm looking out of it... and Bolters or other guns are great, too.

I still have lots of transfers from the early Rhino Boxed sets, so they can be put to good use on the barrels.

Paint the whole thingie black with acrylics. Then drybrush with silver. After this is really dry (!), use your Rust-Mix to get a wheathered look. Open barrels can be decorated with cotton wool to represent burning oil drums.